Once in a Blue Moon
Fact and fantasy about blue Moons.
"According to old folklore," some people
say, the second full Moon in a calendar month is called a "blue Moon." They go
on to explain that this is the origin of the expression "once in a blue Moon."
But it isn't true! The term "blue Moon" has been around a long time, well over
400 years, but its calendrical meaning has become widespread only in the last
A Variety of Meanings
In fact, the very earliest uses of the term were remarkably like saying the
Moon is made of green cheese. Both were obvious absurdities, about which there
could be no doubt. "He would argue the Moon was blue" was taken by the average
person of the 16th century as we take "He'd argue that black is white."
The concept that a blue Moon was absurd (the first meaning) led eventually to
a second meaning, that of "never." The statement "I'll marry you, m'lady, when
the Moon is blue!" would not have been taken as a betrothal in the 18th
But there are also historical examples of the Moon actually turning blue.
That's the third meaning — the Moon appearing blue in the sky. When the
Indonesian volcano Krakatoa exploded in 1883, its dust turned sunsets green
and the Moon blue all around the world for the best part of two years. In
1927, the Indian monsoons were late arriving and the extra-long dry season
blew up enough dust for a blue Moon. And Moons in northeastern North America
turned blue in 1951 when huge forest fires in western Canada threw smoke
particles up into the sky.
So, by the mid-19th century, it was clear that visibly blue Moons, though
rare, did happen from time to time — whence the phrase "once in a blue Moon."
It meant then exactly what it means today, a fairly infrequent event, not
quite regular enough to pinpoint. That's meaning number four, and today it is
still the main one.
But meaning is a slippery substance, and I know of a half dozen songs that use
"blue Moon" as a symbol of sadness and loneliness. The poor crooner's Moon
often turns to gold when he gets his love at the end of the song. That's
meaning number five: check your old Elvis Presley or Bill Monroe records for
And did I mention a slinky blue liquid in a cocktail glass, one that requires
curaçao, gin, and perhaps a twist of lemon? That's number six
Finally we arrive at the most recent meaning of all, the second full Moon in a
month. I first heard it in 1988. At the end of May that year, when a second
full Moon occurred, radio stations and newspapers everywhere carried an item
on this bit of "old folklore," as they called it, drawing on an international
wire story. Across North America the blue Moon caught the public's
imagination. In the following months, restaurants, clothing stores, and
bookstores opened under the name "Blue Moon." An artist I know did a set of
night landscapes that month; he calls them his Blue Moon series. At the
Memorial University of Newfoundland Folklore & Language Archive we get calls
from all over, from people wondering about bits of folklore. And that month we
got calls about blue Moons.
I searched high and low for an earlier example of this usage, or any other
name for two full Moons in a single calendar month. But the search was in vain
— this meaning seemed to have no history. I did find information on the other
meanings of "blue Moon," but not this one, number seven.
Then in December 1990, with another "blue Moon" coming on, I started getting
more calls and decided to write about it in the local newspaper. I searched
harder this time, exhausting all the usual sources: specialized dictionaries,
indexes of proverbial sayings, and regional collections of folklore. A
brand-new edition of the huge Oxford English Dictionary had recently come out,
but even it omitted this particular meaning. "Blue Moon" seemed to be a truly
modern piece of folklore, masquerading as something old.
Then my brother-in-law reminded me that the term was a question in one of the
Trivial Pursuit boxes, the Genus II edition published in 1986. I hope the
manufacturer of this game is still the fine company for scholars it was then.
They had kept all their files and were able to tell me their source had been a
children's book published the previous year, The Kids' World Almanac of
Records and Facts (New York, 1985: World Almanac Publications). Where the
authors, Margo McLoone-Basta and Alice Siegel, got it, no one seemed to know.
Used in this way, the term was certainly very, very local before they included
it in their book. It seemed never to have been written down before. Of course,
authors sometimes "invent" information to protect themselves against
plagiarists. Well, if that were the case they'd already lost, because the new
"blue Moon" almost immediately entered the folklore of the modern world. It
became as living a meaning as any of its predecessors.
During my search it hadn't occurred to me that radio might have played a role.
My newspaper column had just gone to the printer when I got a copy of the
December 1990 Astronomy. There, Deborah Byrd mentioned the term coming from a
March 1946 article in Sky & Telescope (page 3). Contacting her, I found out
she had read it for her National Public Radio program, Star Date, in late
January 1980. No doubt that's where the authors of the children's almanac
heard it. Clearly, Byrd's radio broadcast got the recent "blue Moon" ball
Our new blue Moon has something of the modern times in it, a technical aspect
that most of the earlier meanings lacked. Perhaps that's why it caught on so
quickly. It appeals to our modern sensibilities, including our desire to have
plausible origins. But any folklorist will tell you that plausibility is the
mantle that folklore wears to sneak through history's lines. "Old folklore" it
is not, but real folklore it is. Given its present popularity, it may last a
By Philip Hiscock
What's a Blue Moon? The trendy definition of "blue Moon" as the second full
Moon in a month is a mistake.